JP2002201411A - Coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition for polyester-based coatings low in time-dependent workability deterioration of coating film and excellent in adhesion to the coated object and balance between hardness and workability. SOLUTION: The composition contains (A) 100 pts.wt. of a hydroxy group- containing polyester resin having a number-average molecular weight of 1,000-100,000, (B) 1-40 pts.wt. of a resol type phenol resin-crosslinking agent, and (C) 0.1-5 pts.wt. (in terms of acid amount) of an acid catalyst. In the composition, the polybasic acid component of the said hydroxy group-containing polyester resin contains 0.1-20 mol% of a trivalent or higher polybasic acid or the polyhydric alcohol component of the same contains 0.1-20 mol% of a trihydric or higher polyhydric alcohol. Furthermore, the polyhydric alcohol component contains 1-80 mol% of a specified dihydric alcohol of an asymmetrical structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition having excellent balance between processability and hardness and capable of forming a coating film having excellent adhesion, curability, hygiene properties and boiling water resistance, especially for can coating. It relates to a suitable coating composition.

[0002]

2. Description of the Related Art Conventionally, paints for inner and outer surfaces of cans, inner and outer surfaces of lids, and inner and outer surfaces of caps which require workability include polyester-amino resins, vinyl-amino resins,
Resin-based paints such as vinyl organosols are used.

[0003] In particular, high-molecular linear polyester resin coatings such as polyethylene terephthalate have excellent balance between adhesion to materials and hardness and workability. However, there is a major problem that the temperature of the steel sheet deteriorates with storage time, and it is difficult to use it in applications requiring strict workability such as drawing and ironing.

[0004] It is an object of the present invention to provide a coating composition which does not deteriorate the workability of a coating film in a polyester-based coating over time, and has an excellent balance between adhesion to materials and hardness and workability. is there.

[0005]

Means for Solving the Problems The inventors of the present invention focused on the fact that the above processability was reduced due to the progress of crystallization of the polyester resin, and as a result of diligent studies, it was found that the polymer polyester resin was appropriately branched. And adding a vertically asymmetric dihydric alcohol component represented by the following formula 1 to prevent crystallization of the polyester resin without deteriorating the intrinsic performance of the high-molecular polyester resin. Reached.

That is, (A) the number average molecular weight is 1,000
~ 100,000 hydroxyl group-containing polyester resin 100
A coating composition containing (B) 1 to 40 parts by weight of a resol-type phenolic resin crosslinking agent and (C) 0.1 to 5 parts by weight (as an acid amount) based on parts by weight, and
The hydroxyl-containing polyester resin (A) contains 0.1 to 20 mol% of a tribasic or higher polybasic acid in the polybasic acid component or 0.1 to 20 mol% of a trihydric or higher polyhydric alcohol in the polyhydric alcohol component.
The present invention relates to a coating composition comprising 1 to 80 mol% of a dihydric alcohol represented by the following formula 1 in a polyhydric alcohol component.

[0007]

Embedded image

In the above formula, R ₁ and R ₂ represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₁ and R ₂ are not the same.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the coating composition of the present invention will be described in more detail.

The coating composition of the present invention comprises a hydroxyl group-containing polyester resin (A), a resol type phenol resin crosslinking agent (B), and an acid catalyst (C).

Hydroxyl-Containing Polyester Resin (A) The hydroxyl-containing polyester resin, which is the component (A) in the coating composition of the present invention, contains a hydroxyl group, a dihydric alcohol represented by the following formula 1, and a moderate amount of it. It is a polyester resin with a branched structure.

By containing a specific dihydric alcohol having a vertically asymmetric structure represented by the following formula 1, and by having a branched structure, crystallization of the polyester resin can be suppressed.

Examples of the dihydric alcohol represented by the following formula 1 having such an effect include 2-methyl-1,3
-Propanediol or 2-butyl-2-ethyl-1,
3-propanediol and the like, the amount of which is
1 to 80 mol% in the polyhydric alcohol component, preferably 5 to 80 mol%
A range of 50 mol% is suitable. Further, in order to cause appropriate branching, a polybasic acid having a valency of 3 or more in the polybasic acid component used for synthesizing the polyester resin is 0.1%.
To 20 mol%, preferably 0.5 to 15 mol%, or 0.1 to 3 polyhydric alcohols in the polyhydric alcohol component.
It is suitable to use within the range of -20 mol%, preferably 0.5-15 mol%.

[0014]

Embedded image

In the above formula, R ₁ and R ₂ represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ₁ and R ₂ are not the same.

The hydroxyl group-containing polyester resin may be any of an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins, for example, a urethane-modified polyester resin or a urethane-modified alkyd resin. Among them, an oil-free polyester resin is preferable.

The oil-free polyester resin is mainly an esterified product of a polybasic acid and a polyhydric alcohol.

Examples of the polybasic acid component include phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, hexahydroisophthalic acid, hexahydroterephthalic acid, succinic acid, fumaric acid, adipic acid, and the like. One or more dibasic acids selected from sebacic acid, maleic anhydride, fumaric acid and the like are mainly used. Further, examples of the branched component include tribasic or higher polybasic acids such as trimellitic anhydride, methylcyclohexentricarboxylic acid, and pyromellitic anhydride.
These polybasic acid components can be used alone or in combination of two or more. Further, if necessary, a monobasic acid such as benzoic acid, crotonic acid, pt-butylbenzoic acid and the like are used.

As the polyhydric alcohol component, in addition to the dihydric alcohol represented by the above formula 1, for example, ethylene glycol, diethylene glycol, 1,2-propylene glycol,
1,3-propanediol, 1,4-butanediol,
Dihydric alcohols such as neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6-hexanediol, and 1,4-dimethylolcyclohexane are mainly used, and glycerin and trimethylol are further used as branching components. Trihydric or higher polyhydric alcohols such as ethane, trimethylolpropane, and pentaerythritol are used as needed. These polyhydric alcohols can be used alone or in combination of two or more. Among them, 1,4-dimethylolcyclohexane is excellent in workability, and can be suitably used in a range of 1 to 70 mol%.

The esterification reaction between the acid component and the alcohol component can be carried out by a known method.

The above-mentioned oil-free polyester resin is also obtained by performing a transesterification reaction using a lower alkyl ester of a polybasic acid (eg, methyl ester, ethyl ester, etc.) instead of the polybasic acid in the above esterification reaction. be able to. The transesterification of both components can be performed by a known method.

In the above oil-free polyester resin, the proportion of the aromatic dicarboxylic acid in the dibasic acid component is 80 to 100 mol%, and the proportion of the terephthalic acid in the aromatic dicarboxylic acid is 40 to 100 mol%. Is preferred.

The alkyd resin is obtained by reacting an oil fatty acid by a known method in addition to the acid component and the alcohol component of the oil-free polyester resin. Examples of the oil fatty acid include coconut oil fatty acid and soybean oil fatty acid. Linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, kiri oil fatty acid and the like.

The urethane-modified polyester resin is obtained by reacting the oil-free polyester resin or a low-molecular-weight oil-free polyester resin obtained by reacting an acid component and an alcohol component in the production of the oil-free polyester resin with a polyisocyanate compound. And a known method. The urethane-modified alkyd resin is obtained by reacting the above-mentioned alkyd resin or a low-molecular-weight alkyd resin obtained by reacting each component in producing the alkyd resin with a polyisocyanate compound by a known method. Polyisocyanate compounds used in producing urethane-modified polyester resins and urethane-modified alkyd resins include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, and 4,4'-
Diphenylmethane diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), 2,4,6
-Triisocyanatotoluene and the like.

In the present invention, the hydroxyl group-containing polyester resin (A) has a number average molecular weight of 1,000 to 100,0.
00, preferably 5,000 to 35,000, and a hydroxyl value of 0.5 to 40 mgKOH / g, and more preferably 3 to 2 mgKOH / g.
0 mgKOH / g, glass transition temperature (hereinafter, “Tg point”
10 to 120 ° C., and 4
0 to 80 ° C., an acid value of 20 mgKOH / g or less, preferably 0.1 to 10 mgKOH / g, for ease of handling of the polyester resin, workability of the obtained coating film, hardness,
It is suitable in terms of water resistance, boiling water resistance and the like.

In the present invention, the Tg point is measured by a differential thermal analysis (DSC) using a differential scanning calorimeter, and the number average molecular weight is determined by gel permeation chromatography (G
PC) using a standard polystyrene calibration curve.

Resol-type phenolic resin crosslinking agent (B) The resol-type phenolic resin crosslinking agent, which is the component (B) in the composition of the present invention, is blended with the above-mentioned hydroxyl group-containing polyester resin (A) to cure by crosslinking reaction. Things.

The resol type phenolic resin crosslinking agent (B) in the present invention is obtained by introducing a methylol group by subjecting a phenol component and formaldehydes to a condensation reaction by heating in the presence of a reaction catalyst to introduce a methylol group. It is obtained by partially alkylating a methylol group with an alcohol.

In the production of the resol type phenol resin crosslinking agent (B), a bifunctional phenol compound, a trifunctional phenol compound, a phenol compound having a functionality of 4 or more are used as the starting phenol component. Can be.

The bifunctional phenol compound used for producing the resol type phenol resin crosslinking agent (B) includes:
Examples include trifunctional phenols such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol. Phenol, m-cresol, m-ethylphenol, 3,5-xylenol, m-methoxyphenol, etc., and as the tetrafunctional phenol compound,
Bisphenol A, bisphenol F and the like can be mentioned. These phenol compounds can be used alone or
A mixture of more than one species can be used.

The formaldehyde used in the production of the resol type phenolic resin crosslinking agent (B) includes formaldehyde, paraformaldehyde and trioxane, and they can be used alone or as a mixture of two or more.

The alcohol used for alkyl etherifying a part of the methylol groups of the methylolated phenolic resin has 1 to 8 carbon atoms, preferably 1 to 8 carbon atoms.
Four monohydric alcohols can be suitably used.
Suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, isobutanol and the like.

Resol type phenol resin crosslinking agent (B)
Has an average of 0.5 or more, preferably 0.6 to 3.0 alkoxymethyl groups per benzene nucleus from the viewpoint of reactivity with the hydroxyl group-containing polyester resin (A).

The amount of the resol-type phenolic resin cross-linking agent (B) in the composition of the present invention is determined in consideration of the curability, water resistance, coating film hardness, flexibility and the like of the resulting coating film. A) 1 to 100 parts by weight
Suitably it is in the range of 40 parts by weight, preferably 2 to 20 parts by weight.

Acid Catalyst (C) The acid catalyst, which is the component (C) of the coating composition of the present invention, promotes the curing reaction of the composition of the present invention, and includes, for example, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, Specific examples include acid catalysts such as dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and phosphoric acid, and amine neutralized products of these acids. Among them, the above-mentioned sulfonic acid compounds or amine-neutralized sulfonic acid compounds are preferred.

By blending the acid catalyst (C), not only the curability of the coating film obtained from the composition of the present invention but also the sharpness can be improved. The amount of the acid catalyst is determined based on the amount of the acid (for example, in the case of an amine-neutralized sulfonic acid compound, the amount of the remaining sulfonic acid compound obtained by removing the amine from the neutralized product) in view of the physical properties of the obtained coating film. ) As a hydroxyl group-containing polyester resin (A) 100 parts by weight,
It is suitable that the amount is in the range of 0.1 to 5 parts by weight, preferably 0.2 to 2 parts by weight.

The composition of the present invention comprises a hydroxyl group-containing polyester resin (A), a resol type phenol resin crosslinking agent (B) and an acid catalyst (C) as essential components. And a solvent. The composition of the present invention may further contain, if necessary, other resins for the purpose of modifying the coating film, and may further contain a color pigment, an extender pigment; an anti-agglomeration agent, a leveling agent, and a defoaming agent. Paint additives; and a small amount of a melamine resin curing agent.

As the above-mentioned solvent, the above-mentioned component (A),
Those which can dissolve or disperse each component such as (B) and (C) and other resins used as necessary can be used, and specifically, for example, toluene, xylene, high-boiling petroleum hydrocarbon, etc. Hydrocarbon solvents, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone, ester solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, methanol, ethanol, butanol Such as alcohol solvents, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ether alcohol solvents such as diethylene glycol monobutyl ether, and the like,
These can be used alone or in combination of two or more.

The other resin is used to improve the flexibility of the coating film,
It is blended for the purpose of improving a coating film such as improving adhesion. Examples of other resins include, for example, an ethylene-polymerizable unsaturated carboxylic acid copolymer, an ethylene-polymerizable carboxylic unsaturated acid copolymer ionomer, and the like. The flexibility of the coating can be improved.

The amount of the other resin is 30 parts by weight or less based on 100 parts by weight of the hydroxyl group-containing polyester resin (A), and particularly from the viewpoint of improving the flexibility of the coating film and boiling water resistance. Preferably, it is in the range of 5 to 20 parts by weight.

The composition of the present invention can be applied to various objects such as metal plates, plastics and glass plates.

The composition of the present invention can be applied to the outer surface and / or inner surface of a metal plate or a can prepared by processing the metal plate and baked to form a coating film suitable for can coating.

Examples of the metal plate used for the above-mentioned cans include beverage cans,
Any metal plate that can be used for a can, a lid, and a cap can be used, and examples thereof include an aluminum plate, a tin-free steel plate, and a tin plate.

The composition of the present invention can be coated by a known coating method such as roll coater coating or spray coating. The coating film thickness is not particularly limited, but is in the range of 3 to 18 μm in dry film thickness. It is preferred that The baking conditions for the coating film are usually such that the maximum temperature of the metal plate is about 90 °.
It is about 5 seconds to about 30 minutes at a temperature of about 300 ° C.

[0045]

The present invention will be described more specifically with reference to the following examples. Hereinafter, “parts” and “%” are based on weight.

Production example 1 of hydroxyl-containing polyester resin (A) 25.62 parts of terephthalic acid, 25.62 of isophthalic acid
5.26 parts, hexahydroterephthalic acid 26.54 parts, ethylene glycol 14.95 parts, 2-methyl-1,3-propanediol 17.36 parts, trimethylolpropane 6.
58 parts and a polycondensation catalyst were charged, and the esterification reaction was carried out while removing water generated by heating and stirring. The number-average molecular weight was 5,000, the hydroxyl value was 58.7 mgKOH / g, and the acid value was 10.0 mgKOH / g. A resin was obtained. The obtained resin was diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 to obtain a polyester resin (A-1) solution having a solid content of 30%.

Production Example 2 24.62 parts of terephthalic acid, 24.62 of isophthalic acid
Parts, 25.51 parts of hexahydroterephthalic acid, 20.11 parts of ethylene glycol, 2-butyl-2-ethyl-
14.83 parts of 1,3-propanediol, 6.33 parts of trimethylolpropane and a polycondensation catalyst were charged and heated.
The esterification reaction was performed while removing water generated by stirring, and the number average molecular weight was 5,000 and the hydroxyl value was 56.8 mgK.
A resin having an OH / g and an acid value of 10.0 mgKOH / g was obtained.
The obtained resin was diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 to obtain a polyester resin (A-2) solution having a solid content of 30%.

Production Example 3 26.40 parts of terephthalic acid, 26.40 of isophthalic acid
, 27.36 parts of hexahydroterephthalic acid, 15.10 parts of ethylene glycol, 21.92 parts of 2-methyl-1,3-propanediol and a polycondensation catalyst, and the resulting water was removed by heating and stirring. The esterification reaction was performed while the number average molecular weight was 1,600 and the hydroxyl value was 21.2 m.
A resin having gKOH / g and an acid value of 10.0 mgKOH / g was obtained. The obtained resin was diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 to obtain a solid content of 30%.
(A-3) was obtained.

Production Example 4 25.44 parts of terephthalic acid, 25.44 of isophthalic acid
Parts, hexahydroterephthalic acid 26.36 parts, 1,3-
32.76 parts of propanediol, 6.54 parts of trimethylolpropane and a polycondensation catalyst were charged, and an esterification reaction was carried out while heating and stirring to remove generated water, a number average molecular weight of 5,000 and a hydroxyl value of 58. 4mgKOH /
g, a resin having an acid value of 10.0 mgKOH / g. The obtained resin was treated with methyl ethyl ketone / cyclohexanone = 50.
The mixture was diluted with a / 50 mixed solvent to obtain a polyester resin (A-4) solution having a solid content of 30%.

Production Example 5 25.62 parts of terephthalic acid, 25.62 of isophthalic acid
5.26 parts, hexahydroterephthalic acid 26.54 parts, ethylene glycol 14.95 parts, 2-methyl-1,3-propanediol 8.68 parts, 1,4-dimethylolcyclohexane 13.31 parts, trimethylolpropane 6. 58
And a polycondensation catalyst were charged, and the esterification reaction was carried out while removing water generated by heating and stirring. The number average molecular weight was 5,100, the hydroxyl value was 53.4 mg KOH / g, and the acid value was 1
0.0 mg KOH / g resin was obtained. The obtained resin was diluted with a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 to obtain a polyester resin (A-5) solution having a solid content of 30%.

The resol type phenolic resin crosslinking agent (B)
Production Production Example 6 100 parts of bisphenol A, 178 parts of 37% aqueous formaldehyde solution and 1 part of caustic soda were added, reacted at 60 ° C. for 3 hours, and dehydrated at 50 ° C. under reduced pressure for 1 hour. Then, 100 parts of n-butanol and 3 parts of phosphoric acid were added, and
The reaction was performed at 0 to 120 ° C for 2 hours. After the completion of the reaction, the resulting solution was filtered to remove the generated sodium phosphate, thereby obtaining a resol-type phenol resin crosslinking agent (B-1) solution having a solid content of about 50%. The resin obtained had a number-average molecular weight of 880, an average number of methylol groups of 0.4 and an average number of butoxymethyl groups of 1.0 per benzene nucleus.

Production Examples 7 to 9 The same procedures as in Production Example 6 were carried out except that 100 parts of the phenol component shown in Table 1 below were used instead of 100 parts of bisphenol A, and each resol type having a solid content of about 50% was used. A phenolic resin crosslinking agent solution was obtained.

Production Example 10 A flask was charged with 188 parts of phenol and 324 parts of a 37% aqueous formaldehyde solution and heated to 50 ° C. to uniformly dissolve the contents. Next, after zinc acetate was added and mixed to adjust the pH of the system to 5.0, the mixture was heated to 90 ° C. and reacted for 5 hours. Then, the mixture was cooled to 50 ° C., a 32% aqueous solution of calcium hydroxide was slowly added to adjust the pH to 8.5, and the reaction was carried out at 50 ° C. for 4 hours. After the reaction, 20
After adjusting the pH to 4.5 with a 1% aqueous hydrochloric acid solution, xylene /
The resin component was extracted with a mixed solvent of n-butanol / cyclohexane = 1/2/1 (weight ratio) to remove the catalyst and neutralized salt, and then azeotroped and dehydrated under reduced pressure to obtain a nonvolatile content of 50%.
A pale yellow transparent phenol resin solution (B-5) was obtained. The obtained resin (solid content) has a number average molecular weight of about 320.
The average number of methylol groups per benzene nucleus is 1.3
And the average number of alkoxymethyl groups was 0.2.

Table 1 below shows the number average molecular weight, the average number of methylol groups and the average number of alkoxymethyl groups per benzene nucleus of each of the phenolic resins obtained in Production Examples 6 to 10.

[0055]

[Table 1]

Phenol component in Table 1 (starting material)
, BPA, BPF, m-CS, p-CS, ph
Means the following phenolic compounds, respectively.

BPA: bisphenol A BPF: bisphenol F m-CS: meta-cresol p-CS: para-cresol ph: phenol (phenyl carbonate)

Example 1 A solution 283 of the polyester resin (A-1) obtained in Production Example 1
In 30 parts (85 parts in solid content), 30 parts (15 parts in solid content) of the phenolic resin (B-1) solution obtained in Production Example 5, 1.0 part of carnauba wax and "Nailure 5225"
(* 1) 4.0 parts (1.0 parts by weight of dodecylbenzenesulfonic acid) were mixed and dissolved, and then a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 (weight ratio) was added to obtain a solid content of 30%. Paint was obtained.

(* 1) Nail Cure 5225: manufactured by King Industries, USA, trade name, amine neutralized solution of dodecylbenzenesulfonic acid, dodecylbenzenesulfonic acid content: 25%.

Examples 2 to 11 and Comparative Examples 1 to 6 The same procedures as in Example 1 were carried out except for using the formulations shown in Table 2 below to obtain paints having a solid content of 30%. The amounts of each component in Table 2 are based on the solid content. However, the amount of Nailure 5225 is indicated by the amount of dodecylbenzenesulfonic acid.

(Note) in Table 2 has the following meaning.

(* 2) Cymel 303: a methyl etherified melamine resin solution manufactured by Mitsui Cytec.

Preparation of Test Coated Plate The coating compositions obtained in the above Examples and Comparative Examples were applied to a thickness of 0.2
8mm dry film weight on 7mm # 5182 aluminum plate
Roll coating was performed so as to be 0 to 90 mg / 100 cm ^2, and it was passed through a hot air drying furnace of a conveyor conveyance type and baked to obtain a test coated plate. The baking conditions were such that the maximum material temperature (PMT) was 255 ° C. and the passage time in the drying furnace was 20 seconds. Various tests were performed on the obtained test coated plate based on the following test methods. The test results are shown in Table 2 below.

Test Method Coating Appearance: The coating appearance of the test coated plate was observed with the naked eye. Good (○) was given when no abnormalities in the coated surface such as repelling, dents, cloudiness and turbidity were observed on the coated surface.

Initial workability: After the test coated plate was prepared, it was left in a room at 20 ° C. for 1 hour, and a special goby fold type Dupont impact tester was used in the room at 20 ° C. An aluminum plate having a thickness of 0.3 mm was sandwiched between the bent portions of the test coating plate which was folded in two, and placed on a tester. A 1 kg thick iron weight having a flat contact surface was placed at a height of 50 cm.
After applying a voltage of 6.5 V to the bending tip for 6 seconds after applying a shock to the bending part by dropping from above, the current value (mA) of the bending tip 2 mm width was measured, and based on the following criteria. evaluated. ：: Current value is less than 2.0 mA, ：: Current value is 2.0 mA or more and less than 8.0 mA, Δ: Current value is 8.0 mA or more and less than 20.0 mA, ×: Current value is 20.0 mA or more.

Temporal workability: Within 5 hours after preparing the test coated plate, put each one in a constant temperature room at 5 ° C., 20 ° C. and 40 ° C., store for one month, and then leave in a room at 20 ° C. for 1 hour. A workability test and evaluation were performed in the same manner as in the initial workability test.

Curability: A test coated plate having a coating area of 100 cm ² was subjected to an extraction treatment in 100 cc of methyl ethyl ketone under reflux for 60 minutes, and the unextracted coating film residue was evaluated according to the following criteria. ：: Residue of coating film is 90% or more ○: Residue of coating film is 75% or more and less than 90% △: Residue of coating film is 40% or more and less than 75% ×: Residue of coating film is less than 40% Adhesion: After immersing the test coated plate in water and treating in an autoclave at 125 ° C. for 30 minutes, JIS K
-5400 8.5.2 (1990) According to the grid-tape method, 11 parallel vertical straight lines each having a length and width of 11 mm were drawn on the surface of the coating film of the test plate so as to reach the substrate with a cutter knife. Draw at intervals and add 1 mm x 1 mm squares to 10
0 were created. A cellophane adhesive tape was adhered to the surface, and the degree of peeling of the squares when the tape was abruptly peeled was observed and evaluated according to the following criteria. ：: No peeling of the coating film was observed at all. ○: The coating film was slightly peeled, but 95 or more squares remained. Δ: 70 or more squares and less than 95 squares without peeling ×: Peeling off Less than 70 squares remained.

Retort whitening resistance: The test coating plate was immersed in water and treated in an autoclave at 125 ° C. for 30 minutes to evaluate the whitening state of the coating film according to the following criteria. ：: no whitening was observed at all; ○: very slight whitening was observed; Δ: slight whitening was observed; ×: significant whitening was observed.

Hygiene: The test coated plate and the activated carbon-treated tap water were put into a heat-resistant glass bottle at a ratio of 1 cc of the activated carbon-treated tap water to 1 cm ² of the test coated plate, and the lid was closed. The solution was treated in an autoclave at 125 ° C. for 30 minutes, and the inner solution after the treatment was evaluated for hygiene based on the consumption amount (ppm) of potassium permanganate according to the test method described in the Food Sanitation Law. . ：: consumption is less than 2 ppm, ○: consumption is 2 ppm or more and less than 5 ppm, Δ: consumption is 5 ppm or more and less than 10 ppm, ×: consumption is 10 ppm or more.

Flavor property: The test coated plate was placed in a heat-resistant glass bottle such that the coating area: tap water treated with activated carbon was 1 cm ² : 1 cc, covered, and sterilized at 125 ° C. for 30 minutes. The solution was subjected to a flavor test and evaluated according to the following criteria. ◎: No change in flavor was observed. ：: Slight change was detected. Δ: Remarkable change was recognized. X: Remarkable change was recognized.

[0071]

[Table 2]

[0072]

EFFECTS OF THE INVENTION The coating composition of the present invention is excellent in balance between processability and hardness, excellent in adhesion, curability, hygiene, flavor and boiling water resistance, and hardly deteriorates in processability over time. An invisible coating film can be formed. Accordingly, the coating composition of the present invention is suitable as a coating for can coating on the inner and outer surfaces of the can, the inner and outer surfaces of the lid, and the inner and outer surfaces of the cap.

Continuing on the front page (72) Inventor Hiroyasu Matsuki 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture Inside Kansai Paint Co., Ltd. (72) Inventor Hideki Matsuda 4-171-1, Higashi-Yawata, Hiratsuka-shi, Kanagawa Kansai Paint stock In-company (72) Inventor Reijiro Nishida 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa F Kansai Paint Co., Ltd.F-term (reference) 4J038 DA052 DA072 DD071 DD121 DD231 DD241 GA03 JC13 KA04 KA06 MA12 MA13 MA14 NA01 NA04 NA11 NA12 PA19 PB04 PC02

Claims (4)

[Claims] (A) a number average molecular weight of 1,000 to 100,
(B) resol-type phenolic resin crosslinking agent 1 to 40 with respect to 100 parts by weight of hydroxyl group-containing polyester resin
1 part by weight and (C) a coating composition containing 0.1 to 5 parts by weight (as an acid amount) of an acid catalyst, and wherein the hydroxyl group-containing polyester resin (A) has a trivalent or higher valency in a polybasic acid component. 0.1-20 mol% of a polybasic acid or 0.1-20 mol% of a trihydric or higher polyhydric alcohol in a polyhydric alcohol component, and a dihydric alcohol represented by the following formula 1 is a polyhydric alcohol. A coating composition comprising 1 to 80 mol% of the components. Embedded image In the above formula, R ₁ and R ₂ are a hydrogen atom or a group having 1 to 4 carbon atoms.
And R ₁ and R ₂ are not the same. 2. The dihydric alcohol represented by the formula (1)
-Methyl-1,3-propanediol or 2-butyl-
2. The compound according to claim 1, which is 2-ethyl-1,3-propanediol.
The coating composition according to any one of the preceding claims. 3. The coating composition according to claim 1, wherein the hydroxyl group-containing polyester resin (A) further comprises 1,70 mol% of 1,4-dimethylolcyclohexane in the polyhydric alcohol component. 4. The coating composition for can coating according to claim 1, wherein the coating composition is a can coating composition.